As is well known, laser sources, particularly solid state lasers, are pumped optically. Light of a suitable wavelength is fed as excitation energy to the laser medium. When a high power laser is pumped, flash devices in the form of gas filled discharge lamps are used to provide such energy. Such flash lamps are ionization path devices and inasmuch as the laser is of elongate form, it is typically necessary to optically couple these to each other by locating the lamp and the laser within an elliptical or cylindrical chamber at the location of the respective focal points.
In the face pumped slab laser, a piece of rectangular solid state laser host material is placed in a housing with a light wave passing through the wide faces of the host material. Atoms in the host material are stimulated by a suitable radiation source such as a pair of lamps, and the interaction of the light wave with the host material atoms produces excitation at the fundamental wavelength of the medium.
The host material or solid state laser material may comprise a slab of Neodymium doped glass having a rectangular cross-section and highly polished side and end faces. The end faces through which the light wave passes are normally inclined at an angle with respect to the side surfaces. The slab is placed in a housing with the end faces exposed. A suitable pair of lamps may be mounted in the housing in alignment with the slab, for providing the radiation pumping to the atoms in the slab.
Because of the intense heat generated in pumping the host material, a coolant fluid is passed through the housing to remove heat. The coolant fluid is caused to pass along the sides of the slab, but the end surfaces must be sealed from the coolant.
Depending upon the operating conditions, the lamps have a limited operating life and, moreover, after a certain length of time of operation, the light output from a lamp can be expected to decrease. In addition to the natural aging of a lamp, sudden failure occurs as caused, for instance, by glass envelope breakage or similar sudden defects.
With presently known devices, the replacement of either a single lamp or a pair of lamps causes an annoying interruption of the laser operation. In order to exchange a lamp, the laser must be switched off and together with manual procedures required to replace the lamp or lamps in the chamber, the interruption may last an undesirable length of time.
If a laser source is used in production, the interruption of service for replacing a lamp causes undue delays and increased production costs. Obviously, given the present state of the art, such interruptions are unavoidable and have been accepted as a necessary fact of life. In order to overcome such interruptions, particularly those caused by aging of the lamp, it is possible to exchange lamps after a certain number of operating hours during scheduled shutdowns of production. In the latter case full advantage is not taken of the actual useful service life of a lamp and replacement costs are unnecessarily increased. While signal devices are known which indicate a decrease of the light output of the lamp in use, such devices do not overcome the need for a shutdown of operations for the sole purpose of replacing a lamp.
Current designs for dual flashlamp cavity boxes (pump cavities) require that the pump cavity assembly be removed in order to "change out" flashlamps. When the assembly is removed, normally the clean volume of the optical bed is violated, exposing all optical components to contamination. This requires, after the flashlamps are changed, that the optical bed volume be purged with dry Nitrogen after the cavity box assembly has been replaced. Even more consequential is the fact that the optical alignment of the laser slab or laser rod at re-installation, i.e., the re-positioning of the slab or rod with respect to the rest of the optics train, is critical to laser system output and performance. Even in laboratory conditions or "clean rooms," any dust particles, dirt, sand, etc. that may fall between any two mating surfaces may well be sufficient to critically misalign the slab or rod. Attempting to accomplish a flashlamp change in a field environment substantially increases the contamination risk such that the laser system may not supply adequate output, and in some instances, the misalignment may be severe enough to entirely preclude lasing.
Another important consideration is the contamination of optical surfaces. Any such contamination will result in burned optical components due to the very high energy levels present in the resonator.
One such solution to the logistic issues involved in utilizing a laser in the field may entail the use of a "portable clean room" with special tools and an adequate supply of dry Nitrogen. Any current implementation of such ideas is unclear. The presently accepted procedure for changing flashlamps is to remove the entire laser transmitter and change flashlamps in the nearest suitable facility, by a specially trained technicians. Many hours as well as a considerable amount of "down time" is necessarily involved. Provisioning spare pump cavity assemblies is a complex issue that up until the present invention has been without an inexpensive solution.